1. Field of the Invention
This invention relates to an oscillation circuit, an electronic circuit using that oscillation circuit, and a semiconductor device, electronic equipment, and timepiece using that oscillation circuit or electronic circuit.
2. Description of Related Art
Oscillation circuits that use crystal oscillators are widely employed in the art in devices such as portable timepieces, portable telephones, and computer terminals. It is necessary to design such portable items of electronic equipment in such a manner that they have reduced power consumptions and longer battery lives.
From the viewpoint of reducing power consumptions, the present inventors have analyzed the power consumptions of electronic circuitry used in portable items of electronic equipment, particularly wristwatches. It has been determined by this analysis that a crystal oscillation circuit consumes a larger proportion of the power consumption than other parts of electronic circuitry formed on a semiconductor substrate. In other words, reducing the power consumption of the oscillation circuit within electronic circuitry used in portable electronic equipment will be an effective method of increasing the lifetime of the battery used therein.
If a voltage V.sub.reg is applied to a signal inversion amplifier in such a crystal oscillation circuit, the output of the signal inversion amplifier is inverted in phase by 180 degrees and is fed back and input to the gate thereof. This drives a pair of transistors that form the signal inversion amplifier to turn on and off alternately, the oscillation output of the crystal oscillation circuit gradually increases, until finally the crystal oscillator achieves a stable oscillation.
However, after this stable oscillation has been reached, only a small amount of energy is necessary in comparison with that required for activation, to compensate for losses in inertial energy in the crystal oscillator and thus maintain the oscillation.
In addition, different amounts of energy may be necessary for stable oscillation, even in circuits produced to the same standards, because of variations in the capabilities of signal inversion amplifiers that occur during mass production.
In spite of this, each conventional crystal oscillation circuit is configured in such a manner that the above pair of transistors are always driven alternately on and off at fixed voltages, during activation and also after stable oscillation is achieved. This is a major cause of increased power consumption of the entire circuit.